The present invention relates to a machine for grinding the edges or rim of a spectacle lens, including shaft halves for holding the lens therebetween, a grinding wheel for machining the periphery of the lens, a support means for a template that is held by one of the shaft means, and a measuring head that is connected to a computer and serves for measuring the position of the front and rear sides of the lens at the grinding or contact point, in the vicinity of the periphery of the grinding wheel, relative to a prescribed plane.
U.S. Pat. No. 4,596,091 and the corresponding French Patent No. 2 543 039 disclose a machine of this general type for grinding the edges of a lens that serves for providing a bevel at the edge of the lens. With this known machine, the inner and outer sides of the lens are scanned in the vicinity of the periphery of the lens by two resiliently mounted, pin-like sensors that constantly rest directly against the lens. The axial position of the sensors is communicated to potentiometers, with the values and data determined by these potentiometers being relayed to a computer or a data bank. If the scanning is effected at the same time as the grinding, the heretofore known scanning apparatus causes scratches to occur in the vicinity of the periphery of the lens as a consequence of the particles of the lens that have been ground off. In addition, when the lens is inserted between the two pin-like sensors, it is necessary to retract one of the sensors against spring force in order to provide a gap between the two sensors into which the edge of the lens can be inserted.
In contrast to the heretofore known apparatus, it is an object of the present invention to provide a machine of the aforementioned general type for grinding the edges of a lens, with the inventive machine making it possible to determine the data concerning the curve of the grinding or contact point on the periphery of the grinding wheel, which curve is described by the front and rear edge of the lens, without hereby producing scratches as occurs with the aforementioned known machine.